Separation of close-boiling oxygenated compounds from their liquid mixtures



Patented Apr. 8, 1952 SEPARATION OF CLOSE-BOILING OXYGEN- ATED COMPOUNDS 'FROM THEIR LIQUID MIXTURES Charles E. Morrell, Westfield, N. J., assignor to Standard Oil Development Company, a corporation of Delaware Application October 9, 1950, Serial No. 189,246

This invention relates to a practical method of separating close-boiling oxygenated organic compounds and is concerned with the controlled use of a relatively high-boiling hydrocarbon liquid as a refluxing medium in a continuous fractional distillation of the close-boiling oxygenated compounds.

It has been suggested that a heavy oil be used as an absorbent to effect purification of aqueous alcohols prepared by the hydrolysis of alkyl sulfates. This purification has been effected by passing the vapors of the aqueous alcohol countercurrent to a stream of oil whereby the impurities are dissolved in the oil and removed. It has, however, not been possible to achieve-separation by this method between several materials each of-which is more volatile than the oil and which boil close together.

It is, therefore, an object of this invention to provide a commercially feasible process for the efiicient separation of close-boiling oxygenated compounds which are diflicult to separate by ordinary fractional distillation methods.

The process of this invention is best applied to distillation cuts or mixtures, the components of which distill within a narrow range, however, it may be applied to wide-boiling mixtures as well. The invention is particularly directed to the separation of alcohols as a class or one particular alcohol from other oxygenated compounds such as ketones, acetals, esters, aldehydes, etc. Typical separations which can be made are a mixture of ethyl and isopropyl alcohols from methyl ethyl ketone, ethyl from a mixture of isopropyl alcohol and methyl ethyl ketone, a mixture of ethyl and isopropyl alcohols from other closely boiling oxygenated compounds, and ethyl alcohol from a mixture of isopropyl alcohol with other oxygenated compounds. 7

' The crude oxygenated mixture may contain small amounts of water but in any case it must be miscible with the solvent in all portions of the fractionation zone.

Some of the above-described mixtures are obtained by an olefin hydration reaction, e. g., when a mixture of ethylene and propylene is absorbed in sulfuric acid, diluted, hydrolyzed, and a resulting aqueous alcohol mixture is stripped out. Another important source of such mixtures is the Fischersynthesis hydrogenation of car- 9 Claims. (Cl. 20239.5)

bon monoxide, especially when the aqueous layer product formed contains not only lower primary and secondary alcohols but also various ketones, aldehydes, ethers, acetals, esters, carboxylic acids and certain tertiary alcohols. Still another source is in the product of hydrocarbon oxidation where both oil and water layers are obtained, both containing oxygenated organic compounds. Narrow-boiling range mixtures which may be obtained by the ordinary distillation processes from, aqueous solution are as follows:

7 TABLE I Narrow-boiling range alcohol mixtures Group Components {Ethyl Alcohol isopropyl Alcohol Ethyl Alcohol Isopropyl AlcohoL Methyl Ethyl Ketoner {Ethyl Alcohol isopropyl Alcohol. t-Butyl Alcohol water layer of a Fischer synthesis process contains the following:

TABLE II Ethanol out Compound 2 g g??? Acetone 56. 5 Methyl alcohol 64. 7 n-butyraldehyde 75.7 Ethyl acetate 77. l Ethyl alcohol 78. 5 Methyl ethyl ketone 79. 6 Isopropyl alcohoL 82. 3 t-butyl alcohol 82.8 Normal propanol 97. 2 Methyl propyl ketone. 101. 7 Acetal 103. 2 Water 100. 0

In such crude ethanol cuts, the kinds and relative quantities of the components vary greatly but the major components are generally ethyl alcohol, isopropyl alcohol and methyl ethyl ketone. Repeated fractional distillations of the ethanol cuts were found to be of no avail for effecting isolation of pure ethyl alcohol or pure isopropyl alcohol. The difficulties encountered can be appreciated by reference to Table II which shows the overlapping of the boiling points.

With the present invention it was found possible to effect the critical separations necessary in recovering the pure alcohols freed of the other substances normally boiling in the same narrow range, even though the contaminating substances have relatively lower and higher boiling points.

This is made possible by the discovery that when a mixture of oxygenated compounds, such as any of those mentioned above, are fractionally distilled in the presence of a sufiiciently large volume per cent of a hydrocarbon which is liquid under the conditions existing in the fractionation zone, the normal volatilities of the oxygenated compounds are altered to such an extent that separations which are impossible by ordinary fractionation become possible in the presence of the hydrocarbon. In some cases a compound which is normally more volatile than some other compound is found to become less volatile than the other compound in the presence of a large quantity of a heavy hydrocarbon. For example, acetone is normally more volatile than ethyl alcohol, however, when there compounds are fractionated in the presence of sufiiciently large quantities of a refined white oil, the ethyl alcohol is rendered more volatile and is taken ofi overhead while the acetone is removed as a dilute solution in the oil. On the other hand, other compounds which normally boil close together have their relative volatilities enhanced so that they may be easily separated. For example ethyl and isopropyl alcohol boil close together and cannot be separated by conventional fractionation. However, by distilling these compounds in the presence of sufilciently large quantities of a white oil, the ethyl alcohol is rendered so much more volatile than the isopropyl alcohol that the ethyl alcohol is easily removed overhead and the isopropyl alcohol remains as a bottoms product with no detectible amount of ethyl alcohol present. In general, the alcohols as a class are rendered more volatile in the presence of the hydrocarbon liquid than any of the other oxygenated compounds.

The following tables list the relative volatilities of mxitures of various oxygenated organic compounds in the presence of a white oil.

The relative volatility is the volatility of one component divided by that of the other, the volatility of each component being proportional to its partial pressure divided by its mol fraction in the liquid phase. It is also defined by the equation Alpha=(y1/y2)/(a:1/:c2-) where y refers to the vapor phase mol fractions of thecomponents to be separated and :1: refers to the liquid phase mol fractions of the components to be separated, subscript one designates the more volatile component and subscript two the less volatile component.

TABLE III Relative volatility of various mixtures in the prese ce of awhite oil Relative Volatility of A B Charge Vapor Phase Liquid Phase Over Components Mol Per Vol. Per M01 Per Vol. Per Mol Per V01. Per Without Gent Cent Cent Cent Cent Cent on Oil Ethanol 90.5 89 7 Acetone} B3515 10 9. 5 10 2s 1 09 0 37 figigflsmar Basis. White Oil fi g igg blsinary Basis White on fi figg fi iemnary Basis White Oil 2 }l3inary Basis;.-

30 s sgighly treated kerosene fraction: B. P. 396522 F., Sp. Gr. 0.800, Aniline Pt. 176 F., Flash 160 F., Via/ F.

' TABLE IV Relative volatility of various mz'wtures in the presence of a white oil Relative Volatilit Charge Vapor Liquid Phase A over B y Components l l l o l M01 Vol. Percent M01. Vol. With Without Percent Percent Percent Percent Oil 7 Oil A. Ethanol. 50 55.5 46.0 1.46 1.15 B.- Ispropanol} 50 44.5 54.0 A gifiite (1)il weight percent-. 35 80 arm .11. 40.8 30. 4 1. 58 1. 1' .13. Isopropanol f 65 59.2 69.6 d A Wnte O1l 1 weigl1t pereent 56. 80 72 6 49 nropano .3 3.7 1. 1. 05 B. e 3ui i ii o1} so 27.7 30.3 i e i 90 97.1 A. n-Propanol 3O 34.5 27.0 1.42 1.05 B. se c liutgn ol 70 65.6 73.0 1

1 e i 93.7 A. n-ButanoL- 70 72.2 63.6 1.49 1.05 B. svvmzlfienotaiiol 30 27.8 36.4

- ie i' 90 97.5 A. n-Butanol'. 50 1- 56.2 45.7 1.52 1.05 B. sec-Pentano1} 50 43.8 54.3

White 0' 90 93.8

Highly treated Vii/100 F. 350 SSU TABLE v coastal distillate: B. P. 732924 F., Sp. Gr. 0.885, Aniline Pt. 234 F., Flash 365 F.

Relative volatility of n-propanol Over sec-butanol in the presence of an allcylate bottoms fractzon 1 Mol Per Rel. Vol Equilibrium Vol. Per Mol Per Cent Equilibrium Mixture P hase Cent Oil gi sec-BuOH g ggfi Temp., 0.

Charge 90 1O 1 Vapor 33. 6 91. 9 8. 12 1. 46 120.2.

90 70 33. 6 73. 85 26.15 1. 39 120.2. 94. 0 67. 1 32. 9 90 50 33. 6 56. 1 43. 9 1. 40 120.2. 92.5 47. 7 52. 3 90 30 70 33. 6 37.0 63.0 1. 117.8. 92. 4 27. 5 72. 5 90 10 90 33. 6 12. 7 87.3 1. 43 119.2. 93.0 9. 26 90. 7 90 i 90 10 36.0 91. 9 8. 13 1.46 94. 1 88. 6 11. 46 90 30 37. 4 76. 0 24. 0 1. 6i. 121.2/765 mm. i 94. 1 66.3 33. 7 90 50 50 32.1 59. 7 40. 25 i 1. 118.0/769 mm. 92. 3 45. 54. 15 30 70 33. 0 39. 7 60. 3 1. 79 120.8/765 mm. 92. 3 26. 9 73. 1 90 10 90 35.0 13. 85 86. 15 1. 57 122.6/765 mm. 92. 2 9. 27 90. 7 90 70 30 49. 2 75. 6 24. 4 1. 52 134.9/770 mm. 92. 8 67. 1 32. 9 90 50 50 56.0 56.3 43. 7 1. 38 129.4/763 mm. 92. 0 48. 4 51. 6 90 30 70 46.0 38. 9 61.1 1. 63 130.6/770 mm. 92.0 28.1 71. 9

1 Alkylate bottoms fraction, B. P. 290398 F. by 10% gas oil distillation.

' The data in the above tables indicate quite clearly that the large proportion of hydrocarbon liquid present in the liquid phase as a refluxing medium with the mixed compounds increases the relative volatility and in all but two cases increases the normal volatility ratio, the ratio being reversed for acetone-ethyl alcohol and isopropyl a'lcohol-methol ethyl ketone.

To obtain the desired separation of purified ortioned with benefits of the present invention, the mixture is subjected to a continuous fractional distillation in a column of practical size, including a rectification zone and a stripping zone for countercurrent vapor-liquid contact under reboiling and refluxing conditions. A sufficiently large quantity of hydrocarbon liquid is introduced at an upper part of a rectification zone to effectively modify the relative volatilities of the g'anic components from mixtures like those men- 75 organic compounds to be separated and to distill 7 a larger part of one component or group of components than of another component or another group of components from the internal reflux.

The separation can be effected in a continuous manner under steady state conditions to obtain product streams of desired purities and constant compositions while supplying the large quantity of hydrocarbon liquid to the upper part of the rectification zone. The temperature of the hydrocarbon introduced into the rectification zone is preferably close to the temperature of liquid on its feed plate, although it may be lowered to partially condense vapors ascending to the solvent feed plate.

Since the efficient operation is essentially continuous, the hydrocarbon has to be added continuously near the top of a fractionating column while the mixture of oxygenated organic compounds to be separated is fed continuously into the column at a lowerpoint while sufficient heat is provided to afford distillation throughout 'the column.

The feed stream of the oxygenated organic compounds is preferably introduced into a fractionating column between an upper rectification section and a lower stripping section at a point where the ratio of the main organic compounds to be separated in the feed is similar to the ratio of these compounds in the internal reflux descending through the column.

The feed stream is preferably preheated to a temperature close to that of the internal liquid reflux under practically equilibrium boiling conditions at the point of introduction. The preheated feed stream may be liquid, partially vaporized, or completely vaporized when introduced into the fractionating column.

Vapors of the organic compounds introduced as a feed stream at the bottom part of a rectification zone in a fractionating column pass up through the rectification zone in contact with descending internal liquid reflux under practically equilibrium reboiling and refluxing conditions.

The quantity of solvent required to be introduced continuously at the upper part of the rectification zone for accomplishing the desired separation of the close-boiling compounds is considerably greater than the quantity of condensate with which it becomes homogeneously mixed. This is necessary in order to make the hydrocarbon concentration of the internal reflux substantially above a critical minimum in the range of 70-90 volume per cent. With adequate hydrocarbon concentration in the internal reflux for effectin the separation, the organic component to be isolated in the bottoms is dissolved in the internal reflux that reaches the bottom part of the rectification zone and finally the bottom of the stripping zone.

The minimum hydrocarbon concentration in the internal reflux for obtaining th separation depends on the particular organic compounds to be separated and varies between 70 and 99 volume per cent. In a limiting case of isolating ethyl alcohol from isopropyl alcohol, essentially no separation is effected if the internal reflux contains less than 180 volume per cent hydrocarbon, and for obtaining satisfactory results on a practical scale, more than 90 volume percent hydrocarbon, preferably 90-99 volume per cent solvent, is required in the internal liquid reflux. As the hydrocarbon dilution of the internal reflux becomes infinite, the selectivity of separation is increasedbut the operating efiiciency is excessively lowered on account of the relatively small quantities of the oxygenated organic compounds being processed.

Under steady state conditions existing in a continuously operating fractional distillation zone, the internal reflux having adequate concentration for accomplishing the separation of the close-boiling alcohols and other oxygenated compounds, there tends to be a nearly constant hydrocarbon concentration in the homogeneous liquid phase on each plate above the feed point and on each plate below the feed point although the average concentration on the plates above and below the feed point may differ. This internal reflux in flowing from the top to the bottom becomes richer in the oxygen compounds having the lowest relative volatility in the presence of the hydrocarbon while the oxygen compounds having the highest relative volatility in the hydrocarbon are distilled overhead.

The overhead vapors from the rectification zon are enriched in one or more of the organic components rendered relatively more volatile by the high hydrocarbon concentration in the liquid reflux while the remaining portion of the organic material introduced with the feed remains dissolved in the internal reflux.

The functioning of the stripping zone may be described as follows:

The anhydrous mixture of the close-boiling alcohols and other oxygenated compounds to be separated, as in the liquid reflux from the bottom of the rectification zone, flows downwardly through the stripping zone in countercurrent contact with ascending vapors evolved from the solution under reboiling conditions. A suflicie'ntly high concentration of hydrocarbon is maintained in the liquid flowing down through the stripping zone, as in the rectification zone, to make the liquid progressively richer in oxygenated compounds having the lowest relative volatility in the hydrocarbon while the oxygenated compounds having the highest relative volatility in th hydrocarbon are stripped from the liquid. Under practically equilibrium reboiling and refluxing conditions for complete stripping in the stripping zone, the organic compounds rendered more volatile may be removed as vapor overhead from the stripping zone at the same rate that they enter the stripping zone as part of the liquid feed to this zone and a solution of the organic compounds rendered less volatile freed of the more volatile compounds in the liquid, may be withdrawn from a bottom part of the stripping zone.

Suitable hydrocarbon liquids for use in this process include refined white oils, pure parafiins, o'lefins, naphthenes, aromatics and. mixtures of these. Fractions from virgin or cracked stocks may also be used. The initial boiling point of the hydrocarbons used should not be appreciably lower than that of the highest boiling oxygenated "component to be separated. The final boiling point of the hydrocarbon is not material except that the hydrocarbon must be liquid under the conditions in the tower. However, in order to prevent the formation of azeotrop'es which present operational difficulties, it is preferred to use hydrocarbons which boil about C. but at least 70 C. higher than the highest boiling component to be separated.

In the accomplishment of the foregoing and related ends, the invention then comprises the features hereinafter fully described, and particuularly pointed out in the claims, the following water layer of a Fischer synthesis process.

description and the annexed drawing setting forth in detail certain illustrative embodiments of the invention, these being indicative, however, ofbut a few of the various Ways in which the principle of the invention may be employed.

Figure 1 of the drawing illustrates a flow plan of a unit for obtaining separation between two products, such as for example, between ethyl and isopropyl alcohol in mixtures containing the I same.

Figure 2 illustrates a flow plan on an expanded unit for accomplishing further separations of the products.

Referring to Figure 1, I represents a fractional distillation column in the interior of which is provided means for obtaining efficient counterfraction of this type from which most of the water has been removed, for example, by azeotrope distillation has the following composition:

After removal of the water, this fraction can then be distilled to effect a separation from all material boiling above 100 C. i. e., methylpropyl ketone and acetal. The overhead fraction, consisting of products boiling between 75 and 83 C.

' is suitable as a feed stock for this invention.

Referring to the drawing, this fraction is introduced by line 3 into the tower I where it is fractionated in the presence of a liquid stream of a white oil having a boiling point of 396-522 F.

(200-265 C.) introduced through line A. The conditions in the tower are such as to cause a distillation of the oxygenated compounds in the presence of the oil on each plate of the tower. A sufiicient amount of oil is added so that it is present to theextent of 90 volume per cent on each plate. the column some of them are dissolved in the large excess of oil descending the column and are collected together with the oil in pools on each plate. Conditions are maintained on each plate of the tower such that the liquid mixtures:

of the close-boiling oxygenated v compounds are at their boiling points and are continuously being contacted with vapors boiled from the plates below. Because of the enhanced volatility of the ethyl alcohol in relation to the isopropyl alcohol;

and. other components the vapors are relatively rich in the former and poor in the latter. By maintaining the amount of oil on each plate so large that infinite dilution is approached, the

optimumrelative volatilities for the separation, of the desired components'can be secured. Furthermore, by controlling the amount of oxygenated compound reflux and consequently the rerlux ratio and the number of plates, the actual degree or separation maybe varied until the de- As the vapors of the feed pass up;

sired product purity and recovery are obtained.

Thus a suitable temperature and reflux conditions are maintained in the tower so that'ethyl alcohol appears in the overhead stream and isopropyl alcohol, butyraldehyde, ethyl acetate and methyl ethyl ketone in the bottoms product.

Overhead vapors consisting substantially of pure ethanol are withdrawn from the top of column I through line 5 by whichthey are passed through condenser 6 to a receiver I. A portion of the condensate collected in receiver 1 'is returned to. the top part of the column I as external reflux through line 8. The remaining portion of distillate collected in receiver I is withdrawn through line 9 as a product. Bottoms liquid consisting of a solution of 'isopropyl alcohol, butyraldehyde, ethyl acetate and methyl ethyl ketone in oil collected at the lower part of column I is passed by line I0 into reboiler I I for heating by indirect or direct heat exchange with a heating medium such aslive steam. Aportion of the bottoms liquid heated and partially vaporized in the reboiler II is recycled by line I2 to the lower part of column I. The remaining portion is withdrawn through line I3 to tower 2 where the isopropyl alcohol,

butyraldehyde, ethyl acetate and methyl ethyl ketoneare separated from the oil and removed overheadthrough line I4. Oil is removed from the bottom of the tower through line I5 and recycled to tower I through line I6.

In Figure 2 is shown a diagrammatical flow plan of a modified process forobtaining separate ethyl alcohol and isopropyl alcohol products in substantial purity from an ethanol cut subjected to a multi-stage distillation in large quantities of oil. I I

Referring therefore to this drawing, vapors of an ethanol out having a composition of the type the presence of disclosed above in connection with Figure lfare constituents'including butyraldehyde, ethyl ace- 'tate, methyl ethyl ketone and isopropyl alcohol are taken off in the bottoms as -a dilute solution in the oil. 7

The bottoms fraction is then passed by line I64 to a second distillation tower I05 where it is subjected to another distillation in the presence of greater-than 90 volume per cent of the same oil used in tower IUI In this tower conditions are maintained so that isopropyl alcohol is taken oil overhead and. butyraldehyde, ethyl acetate and methyl ethyl ketone are removed from the bottom in a dilute 'oil solution. The bottoms thus obtained is distilled in tower 'I 06 whereby butyralde- 'hyde and ethyl acetate and methyl ethyl ketone are taken ofi overhead and oil drawn oil' the bottoms for recycle through line I01.

This application is a continuation-in-part of application, Serial Number 768,440, filed August '13, 1947, which more particularly claimslthe method of separating between alcohols by using the hydrocarbon solventreflux for altering the relative volatilities between the alcohols. The

, t o one anothenjfor it has been demonstrated that 1 9v nsti e hy o arb n. s ent min gs ra 11 tive distillations that the volatilities of the different types of compounds are lowered in the following descending order.

Relative volatilities:

(1) Alcohols (highest) (2) Ketones (3) Aldehydes (4) Esters (5) Ethers (6) Hydrocarbons (least) are rendered more volatile than close-boiling aldehydes, esters more than ethers, and ethers more than hydrocarbons. Thus, the order of change in relative volatilities accomplished by using the hydrocarbon in the extractive distillation of such organic compounds is substantially the reverse of the order when using a polar solvent, such as water, in the extractive distillation of such compounds in their close-boiling mixtures. Also with the high hydrocarbon content in the reflux, as between homologs, the lower molecular weight compound is made relatively more volatile, e. g. the relative volatility of acetone with respect to methyl ethyl ketone is increased above the normal value.

The nature and objects of the present invention having been thus fully set forth and specific examples of the same given, what is claimed as new and useful and desired to be secured by Letters Patent is:

tionation zone at a point substantially above the mixture feed point sufficient liquid hydrocarbon solvent which boils at a temperature sufficiently above the boiling points of the alcohol and ketones so that it does not azeotropically distill from the fractionation zone to maintain an internal liquid reflux having a hydrocarbon solvent content in the range of 70 to 99 volume percent and to maintain condensates of the alcohol and ketones homogeneously dissolved in the hydrocarbon solvent present in the internal liquid reflux, distilling from said fractionation zone the alcohol, and leaving the ketones inthe internal hydrocarbon solvent reflux remaining undistilled.

v 2. A process for separating an anhydrous mixtureof ethyl alcohol, isopropyl alcohol, methyl ethyl ketone, butyraldehyde and ethyl acetate,

which comprises fractionally distilling the mix- 1 ture in a first distillation zone in the presence of 90 volume per cent of a refined white oil boil- 1 ing 396-522 F. to produce a distillate comprising ethyl alcohol, and abottoms mixture comprising ethyl acetate, butyraldehyde, isopropyl alcohol, methyl ethyl ketone dissolved in said oil, passing said extract to a second distillation zone where it is fractionally distilled in the presence of greater than 90 volume per cent of 'a white refined oil boiling 396-522 F. to produce a second distillate consisting of isopropyl alcohol in sub- 'stantial purity and a second bottoms mixture "comprising ethyl acetate, butyraldehyde and n-butyl acetate.

methyl ethyl ketone in solution in said oil, passing said second bottoms to a third distillation zone where it is fractionally distilled to produce a third distillate comprising methyl ethyl ketone, ethyl acetate and butyraldehyde and a bottoms oil fraction and recycling said oil to said first and second distillation zones.

3. A process of separating ethyl alcohol from a mixture containing isopropyl alcohol and a ketone higher boiling than the ethyl alcohol, which comprises extractively distilling the ethyl alcohol from said mixture in the presence of a solvent selected from the group consisting of aromatic hydrocarbons, paraflinic hydrocarbons, naphthenic hydrocarbons, and mixtures of said hydrocarbons, which solvent is sufliciently high boiling so that it does not distill with the ethyl alcohol extractively distilled from the mixture while the ketone and isopropyl alcohol are thus separated as residual liquid products in distilling the ethyl alcohol therefrom.

4. A process of separating a C1 to C4 alkanol from a ketone having a closely related boiling point, which comprises extractively distilling the alkanol from a mixture thereof with the ketone in the presence of a hydrocarbon solvent which is sufiiciently high boiling so that it does not distill with the alkanol and maintaining vapors of the alkanol and ketone undergoing distillation in equilibrium with the alkanol and ketone condensate dissolved in a liquid reflux containing '10 to 99 volume percent of the hydrocarbon solvent during the extractive distillation whereby the alkanol is rendered sufliciently more volatile than the ketone for fractionation therefrom.

5. The process described in claim 4, in which the ketone has a normal boiling point lower than of the alkanol rendered relatively more volatile.

6. The process described in claim 5 in which the ketone is methyl ethyl ketone and the alkanol rendered more volatile is a Ca alkanol.

7. A process of separating a saturated unsubstituted aliphatic alcohol having 1 to 4 carbon atoms per molecule from a mixture thereof with carbonyl and ester compounds having normal boiling points lower than and closely related to the boiling point of the alcohol, which comprises extractively distilling the mixture in the presence of a liquid hydrocarbon solvent which is sufliciently high boiling so that it does not distill azeotropically with the alcohol, and maintaining to 99 volume percent of the hydrocarbon solvent in solvent in liquid reflux containing dissolved condensate of said mixture undergoing extractive distillation to increase the volatility of the alcohol.

8. The process of separating a C1 to C4 alkanol from a mixture thereof with ketone and ester compounds having normal boiling points higher than and closely related to the boiling point of the alkanol, which comprises extractively distilling the mixture in the presence of a liquid hydrocarbon solvent which is sufiiciently high boiling so that it does not distill azeotropically with the alkanol, and maintaining -70 to 99 volume percent of hydrocarbon solvent in liquid reflux containing condensate of the mixture undergoing extractive distillation.

9. A process as described in claim 8, in which the alkanol is normal butanol and the ester is CHARLES E. MORRELL.

(References on following page) 13 REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,107,265 Archibald Feb. 8, 1938 2,339,160 Dunn et a1 Jan. 11, 1944 OTHER REFERENCES Seheibel, Principles of Extractive Distillation," Chemical Engineering Progress, vol. 44, pages 927 to 931 (December 1948). 

4. A PROCESS OF SEPARATING A C1 TO C4 ALKANOL FROM A KETONE HAVING A CLOSELY RELATED BOILING POINT, WHEN COMPRISES EXTRACTIVELY DISTILLING THE ALKANOL FROM A MIXTURE THEREOF WITH THE KETONE IN THE PRESENCE OF A HYDROCARBON SOLVENT WHICH IS SUFFICIENTLY HIGH BOILING SO THAT IT DOES NOT DISTILL WITH THE ALKANOL AND MAINTAINING VAPORS OF THE ALKANOL AND KETONE UNDERGOING DISTILLA- 